<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>

  <body>
    <!-- 开发环境版本，包含了有帮助的命令行警告 -->
    <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>

    <div id="app">
      <p>今日温度：{{temperature}}</p>
      <p>穿衣建议：{{this.suggestion}}</p>
      <p>
        <button @click="add">添加温度</button>
        <button @click="reduce">减少温度</button>
      </p>
    </div>

    <script>
      var suggestion = ["T恤短袖", "夹克长裙", "棉衣羽绒服"];

      var app = new Vue({
        el: "#app",
        data: { temperature: 14, suggestion: "T恤短袖" },
        methods: {
          add: function () {
            this.temperature += 5;
          },
          reduce: function () {
            this.temperature -= 5;
          },
        },
        // watch: {
        //   temperature: function (newVal, oldVal) {
        //     if (newVal >= 26) {
        //       this.suggestion = suggestion[0];
        //     } else if (newVal < 26 && newVal >= 0) {
        //       this.suggestion = suggestion[1];
        //     } else {
        //       this.suggestion = suggestion[2];
        //     }
        //   },
        // },
      });
      app.$watch("temperature", function (newVal, oldVal) {
        if (newVal >= 26) {
          this.suggestion = suggestion[0];
        } else if (newVal < 26 && newVal >= 0) {
          this.suggestion = suggestion[1];
        } else {
          this.suggestion = suggestion[2];
        }
      });
    </script>
  </body>
</html>
